Apple is justified doing whatever they want. I even agree with apple's stand that traditional gaming market doesn't matter to them. But from the traditional developers' perspective, Apple system is hostile and they have no reason to develop for Apple. Valve go out of their way to develop proton which is based on vulkan. Apple could utilize it if they have supported vulkan. Valve actively expand the linux support for old and current games. Apple has to work for it to court the traditional developers. Superior hardware doesn't mean much when the alternatives are good enough

And it's justified, because it's really not that important in money making in grand scheme of things.